Various specific combinations of turbines and synchronous generators have been used in the past. In one known type the whole turbine, generator, shaft, coupling (and in some cases gearbox) are placed in one "bulb" or pod, which is all placed in the water flow. All components lose their heat losses in an enclosed space, the water passages become large, and the whole assembly requires massive support structure. Consequently, thermal, hydraulic, mechanical and civil problems must be solved.
In another known type the so-called tube or tubular turbine or pump, only the turbine runner is placed in the flow tube or conduit. This arrangement is not in fact a combination, and, requires a long shaft which has to be supported and sealed, a coupling, often requires a gearbox, and the generator is separate. Hydraulic losses occur due to the bend in the draft tube and sealing of the shaft is necessary. Complications arise due to the number of components to align, erect and balance.
Because the above described prior systems each involve the use of two inherently separate machines, namely a turbine and a generator, each with its own separate rotating assembly; the whole is relatively complex, and the cost in terms of manufacture and maintenance often high. Also the overall dimensions axially are considerable being essentially at least the addition of those of the separate turbine and generator.
One prior machine which uses a single rotating assembly for both the turbine and the generator is the so-called Harza type machine. In this machine the rotor of the generator is mounted on the periphery of the turbine runner blades rather than on the end of the turbine or common shaft. The turbine runner, shaft and bearings are supported in a flow tube or conduit and the generator rotor and stator are located outside the tube. It should be evident that extremely effective sealings and complicated methods for securing the massive generator rotor to the runner blades are necessary. In all the foregoing combinations, and in others described in the literature the electrical and the hydraulic machines are inherently separate.
It is an object of the present invention to provide a novel synchronous machine which overcomes some or all of the above-mentioned disadvantages.